Isocyanate-polyvinyl formal resin composition and coated wire



Unite States PatentOfifice 3,077,462 Patented Feb. .12, 1 963 ISOCYANATE-POLYVINYL FORMAL RESIN COM- This invention relates, to resinous compositions especially adapted to serve as electrical insulation for metals. More particularly, the invention relates to compositions of polyvinyl acetals reacted with certain polyurethanes and to Wires coated with these compositions.

, A number of important uses have developed for polyvinyl acetals since their discovery over twenty years ago. The insulation of electrical conductors with polyvinyl formals modified with phenol-aldehyde resins is one of the major commercial applications. These insulating coatings are used for approximately 70% of the magnet wires manufactured in this country. Nonetheless in certain applications a need exists for a wire enamel possessing greater dielectric breakdown strength in the presence of moisture, greater resistance to the solvent action of certain refrigerants such as chlorodifiuoromcthane (CHClF and one which will permit the ready soldering of coated wires at temperatures below 500 C.

An object of this invention is to provide resinous compositions of urethane modified polyvinyl acetals. Another object is to provide a wire coated with such compositions. K A further object of this invention is to provide in one system a new insulating enamel which has the desirable properties otthe present polyvinyl formal-phenolic compositions and in addition possesses the desired characteristics referred to above. I These and other obi cts are attained by reacting polyvinyl acetals with a polyurethane represented by the general formula 0 H n o v C.H.... Canaan-aux)...

I :Phcuolio resin 4 High solvency pcwhere R represents a member of the class consisting of A' polyvinyl formal resin was used having the' fol-low ing analysis:

acetate. groups calculated as polyvinyl acetate 6.0%"hydroxyl' groups calculated as polyvinyl alcohol 83.5% formal groups calculateda's polyvinyl formal (by diilerence) One hundred parts of this. resin and 133 parts of a polyurethane represented by the formula ,3 I 1, f .hF-C-O-Y] R C raowunnL-o-o-nOdm y where Y is a methyl phenyl group, were dissolved in a mixture of 440 parts of high solvency petroleum hydrocarbon (B.P. ISO-184 C., composed principally of alkyl benzenes) and 258 parts of a commercial cresylic acid (B.P. 207-223' C.). The solution was amber colore and had a viscosity of about poises at 20 C.

Six coats of this enamel were applied to 0.05 inch diameter annealed bright copper wire by running the wire through the solution and then through spring clip dies. After each coating, the wire was passed through 'a vertical oven 12 feet high at a speed of 8 ft./min., the hottest portion being approximately four feet long and having a temperature of about 335? C. The 'enamelled wire so produced is classified by the National Electrical Manufacturers Associationas HF wire, the increase'in diameter due to coating being within therange of 26 to 3.5 mils. p I 1 Enamelled wires were prepared in a like manner using the formulae shown in Examples II-IX (Table l). 1

'Table 1 7 Examples II III IV v VI VII vrn IX Polyvinyl formal of EX.I Polirriuyl formal Polyester resin troleurn hydrocarbon 273 230 635 440 480 374 391 440 Commercial ores ylic acidun. 163 324 302 252 219 229 258 The polyvinyl formal A resin had; an analysis of 13.0%. acetate groups and 7.6% alcohol groups, the balance being formal groups.

The polyester resin was a liquid, low molecular weight alkyd, highly branched and having several OH groups per molecule. a The phenolic resin was a soluble, fusible, heat-hardem able phenol-formaldehyde reaction product dissolved in an. equal weight of cresylic acid. H 3 Example lX illustrates the commercially available high quality insulated magnet wires oithe present time. I

-The enamelled' wires of Examples II X passed the standards, of the National Electrical Manufacturers Association (NEMA) for vinyl. .acetal magnet wire as to flexibility and adhesion. Results of other standard tests on these coated wires are shown in Tables 2. and 3. I

Table 2 1 Tinning Build Dielectric (volts/mil) CHClF': Time Ex. N0. (mils) Strength, wet Blistcring seconds dry Test at 450 2. 9 2, 700 2, 300 1' i J6 2.8 2,900 2,400 1 25 2. 7 2, 900 1,800 1" 20 3. 2 2, 700 2, 700 1-2 I0 2; 8 1, 45 2. 6 2, 900 2, 300 1 11 3. 3 2, 300 1,800 2, 15 2. 2 2, 300 1, 400 4. 40 2. 7 2, 500 1, 400 4 60 Build.-The addition to thediameter of the bare wire, in thousandths of an inch, is measured by means of a micrometer'caliper. I V Dielectric strength, dry-Pairs of wires were twisted togetherS 'turns' over a distance of'4,7 5 under a tension of 3"pbn'1ids. Specimens were conditioned over dried silica gel for 3 days. Voltage was then appliedbetween the wires and increased at ,the rate of 500 volts per seconduntil the insulation was broken down by an arc. The breakdown voltage was then divided by the coating build in mils. The results shown are the average of three tests.

Dielectric strength, wen-The test .was similar to the dry test. However, the twisted wires were conditioned by immersion in water at 25 C. for 24 hours. The wires were removed from the water and tested directly. 4 CHCIF, blistering test.-Specimens were placed in a 'bomb of about 300 cc. capacity and 50 cc. refrigerator oil and 50-75 g. CHCIF; were added. The bomb was kept at 40 C. for 16 hours, opened, and the specimens immediately placed in an oven at 125 C. After 15 minutes the wires were removed, cooled and examined. The resistance of the coating to CHCIF, was rated on a scale from 1 (intact) to 6 (continuous blistering).

Tinning time-Solderability was tested by immersing at least 1" of a specimen of the coated wire in a mixture" of equal parts of tin and lead held at 450 C. The time reported is that required to remove sufiicient insulation to tin the copper 'for at least $6 from the tip.

Table 3 Abrasion Cut- Methanol Toluene Ex. No. Strokes, Through Extract, Resistance 780 g. wgt. Temp., C. Percent 68 295 r 0.22 100+ 96 249 0. 55 100+ 60 1 100+ 80 100+ 96 100+ 89 259 0.94 100+ 60 232 1.3 2 3 182 9.0 v 3 93 208v 2.1 100+ l Abrasion with a 550 g. weight wore through the coating in 46 strokes.

' Abrasion resistance.-A specimen was wiped with a clean cloth and then elongated about 1% to removekinks. A NEMA-General Electric Abrasion Scrape Tester repeatedly scraped the specimen with the cylindrical surface of a steel needle 0.016" in diameter, for a length of at a rate of 60 strokes per minute until the coating was worn through. A weight of 78 g. was applied through the needle.

Cut-through temperature-A load ,of pounds was applied at the junction of two pieces of enamelled wire crossing at 90. The temperature was raised at a rate of C. per minute until shorting of the junction closed a twelve volt bell circuit. I

Methanol extract.-A 20 g. specimen was dried and weighed (A). It was then immersed in 150 ml. boiling methanol for two hours, rinsed in fresh methanol, dried and re-weighed (B). The coating was then stripped off and the bare wire dried and weighed (C). Methanol extract,

oom-B) Percent- Toluer'tc' resistance-Specimens were immersed-24 hours in toluene at 25 C., then placed in a NEMA-G.E. Abrasion Tester under a 400 g. load until the coating was worn through.

' The resinous compositions of this invention may' be the reaction product of 100 parts by weight of a polyvinyl acetal and 18-400 parts by weight of a polyurethane. For :insulative wire coating compositions it is preferred to react 100 parts of a polyvinyl formal with 43-150 parts of a polyurethane. 5 J

' The polyurethanes of this invention may be prepared pounds contain-ingnot morethan 16 carbon atoms. For

use in wire enamels, the polyhydric alcohols should contain not more than 10 carbon atoms. Examples of these alcohols are ethylene glycol, propylene glycol, glycerol, trimethylol propane, pentaerythritol, one of the isomeric hexanetriols, etc. The monohydric phenol may be an aryl compound such as phenol, cresols, xylenols and ethyl phenol. Useful diisocyanates are arylene compounds such as tolylene diisocyanate, phenylene diisocyanate,

.naphthylene diisocyanate and diphenylmethane diiso' .cyanate.

The polyvinyl formal-s useful in this invention are obtained by reacting polyvinyl alcohol or a partially hydrolyzed polyvinyl ester with formaldehyde. Polyvinyl formals contain a certain number of hydroxyl groups and may contain a certain number of ester groups depending upon the extent of the hydrolysis and acetalation reactions. The preferred polyvinyl formal resins contain on a weight basis, 135% ester groups calculated as polyvinyl ester, Ii-15% hydroxyl groups calculated as polyvinyl alcohol and the balance substantially formaldehyde acetal. In the commercial .polyvinyl formals, the ester groups are acetate groups. Other polyvinyl acetals such as the reaction products of hydrolyzed polyvinyl esters with acetaldehyde, propionaldehyde, butyraldehyde and benzaldehyde, may be reacted with the polyurethanes of this invention.

' To be used as a coating composition, the polyvinyl formals and polyurethanes should be dissolved in a substantially anhydrous organic solvent medium. The solvent medium should contain a substantial amount of a phenol such as phenol, cresols, xylenols, and a aliphatic or aromatic hydrocarbon such as xylene, naphtha, and mixtures such as the high solvency petroleum hydrocarbon used in the examples.

The coatings may be applied on metals such as copper, aluminum, zinc, alloys of these metals, or copper plated with nickel, cobalt or tin, by conventional wire coating means.

Polyvinyl female and the polyurethanes used in this invention are both stable when in the dry state. A solution of these materials in an inert substantially anhydrous solvent system at room temperature is also stable. However, noinitiator other than heat is required to accomplish the reaction of the resins. The reaction initiates at temperatures above about 150 0., however,

a temperature of at least 200" C. is preferred for faster added either to the dry starting materials or to the solutions of reactants. r

The resins of this invention form valuable insulative coatingsboth on magnet wires and in other applications such as, for example, foil condensers. These coatings are smooth, glossy, tough, adhere well to metals, are reby reacting a polyhydric alcohol with an equivalent J3 amount ofa reaction product of one mol of a monohydric phenol with one mole of arylene diisocyanate. The polysistant to solvents and abrasion, and are superior to conyentional wire enamels in solderability, resistance to refrigerants such as CHClF and show less loss of dielectric strength on exposure to moisture.

. Moldings may also be formed from these resinous compositions by mixing thereactants in a dry, finely powdered form and thereupon curing the mixture at temperatures above under pressure. Cast articles may be prepared from solutions containing the polyurethane and polyvinyl acctal by pouring the solution into a mold, removing the solvent at temperatures below 150 C. and then curing the casting'at temperatures above 150' C.

What is claimed is:

l. A coating composition comprising an organic solvent solution of 100 parts by weight of a polyvinyl acetal and 18-400 parts by weight of a polyurethane represented by the general formula G,H..,...( O t l R t t O X), where R represents a member of the class consisting of phenylene, methyl phenylene, naphthylene and methyl naphthylene groups, X represents a member of the class consisting of phenyl and alkyl phenyl groups, said alkyl groups containing l-6 carbon atoms, m is an integer greater than 1 but not greater than n, and n is an integer from 2-l0, said solvent comprising a substantial amount of (1) a compound selected from the group consisting of phenol, cresols and Xylenols and (2) a compound taken from the class consisting of aliphatic and aromatic hydrocarbons.

2. A coating composition as in claim 1 wherein the polyvinyl acetal is polyvinyl formal.

3. A coating composition comprising an organic solvent solution of 100 parts of polyvinyl formal and 43-150 parts of a polyurethane represented by the formula H 0 AHLOJ 0 H Where Y is a methyl phenyl group, said solvent comprising a substantial amount of (1) a compound selected from the group consisting of phenol, cresols and xylenols and (2) a compound taken from the class consisting of aliphatic and aromatic hydrocarbons.

4. A composition comprising the cured resinous product of heating, at above 150 C., 100 parts of a polyvinyl acetal and 18-400 parts of a polyurethane represented by the general formula 0 H 11 o It I I ll where R represents a member of the class consisting of phenylene, methyl phenylene, naphthylene and methyl naphthylene groups, X represents a member of the class consisting of phenyl and alkyl phenyl groups, said alkyl groups containing 1-6 carbon atoms, In is an integer greater than 1 but not greater than n, and n is an integer from 2-10.

5. A composition as in claim 4 wherein the polyvinyl acetal is polyvinyl formal.

6. A composition comprising the cured resinous product of heating, at above 150 C., 100 parts of polyvinyl formal and 43-150 parts of a polyurethane represented by the general formula where R represents a member of the class consisting of phenylene, methyl phenylene, naphthylene and methyl naphthylene groups, X represent a member of the class consisting of phenyl and alkyl phenyl groups, said alkyl groups containing 1-6 carbon atoms, m is an integer greater than 1 but not greater than n, and n is an integer from 2-10.

7. A composition comprising the cured resinous reaction product produced by heating at temperatures over 200 C., an organic solvent solution containing 100 parts of polyvinyl formal and 43-150 parts of a polyurethane represented by the formula ii i olrnctonat -o-c-N-om where Y is a methyl phenyl group, said solvent comprising a substantial amount of 1) a compound selected from the group consisting of phenol, cresols and xylenols and (2) a compound taken from the class consisting of aliphatic and aromatic hydrocarbons.

8. A composition comprising the cured resinous reac tion product of heating at temperatures over 200 C., an organic solvent solution containing parts of polyvinyl formal and 43 parts of a material represented by the formula H o f O H his-.. C2H5C (CHflaL-O--ILT- on,

where R represents a member of the class consisting of phenylene, methyl phenylene, naphthylene and methyl naphthylene groups, X represents a member of the class consisting of phenyl and alkyl phenyl groups, said alkyl groups containing 1-6 carbon atoms, m is an integer greater than 1 but not greater than n, and n is an integer from 2-10, said solvent comprising a substantial amount of (1) a compound selected from the group consisting of phenol, cresols and xylenols and (2) a compound taken from the class consisting of aliphatic and aromatic hydrocarbons.

10. A process for insulating wire which comprises coating the wire with an organic solvent solution comprising 100 parts of polyvinyl formal and 43-150 parts of a polyurethane represented by the general formula where R represents a member of the class consisting of phenylene, methyl phenylene, naphthylene and methyl naphthylene groups, X represents a member of the class consisting of phenyl and alkyl phenyl groups, said alkyl groups containing l-6 carbon atoms, m is an integer greater than 1 but not greater than n, and n is an integer from 2-10, said solvent comprising a substantial amount of (1) a compound selected from the group consisting of phenol, cresols and xylenols and (2) a compound taken from the class consisting of aliphatic and aromatic hydrocarbons, and thereafter simultaneously removing the solvent from the coating and curing the coating on the wire at a temperature of at least 200 C.

11. The insulated wire produced by the process of claim 10.

12. A wire coated with a composition which is the reaction product of 100 parts by weight polyvinyl formal and 43 to parts by weight of the urethane of the formula:

wherein R is a phenyl radical and R is va methyl phenylcured mixture of 20-80 parts of a reactive isocyanate, 5

10-70 parts of a polyvinyl formal; and 1040 parts of a ene radical. polyester, said coating being cured on the conductorr 13. An electrical conductor insulated with a hard, r I v flexible, tough and abasi on-resistant coating comprising a 1 References c In the of thls Patent 4 UNITED STATES PATENTS 2,532,011 Dahlqnist et 31. Nov. 28, 1950 

1. A COATING COMPOSITION COMPRISING AN ORGANIC SOLVENT SOLUTION OF 100 PARTS BY WEIGHT OF A POLYVINYL ACETAL AND 18-400 PARTS BY WEIGHT OF A POLYURETHANE REPRESENTED BY THE GENERAL FORMULA 